This invention relates to electrophilic reactions and reactants, and more particularly to a process for generating useful electrophiles, E.sup.+, from common anions, E.sup.-.
Electrophilic addition/substitution of aromatic systems is a field of chemistry that has been widely studied (1-4). Specific examples of reactions having electrophilic mechanisms include halogenation, thiocyanation and nitration.
Reagents for electrophilic halogenation are available in numerous forms ranging from the diatomic element to some fairly exotic halogen delivery reagents (1-5). Most of these reagents are necessarily prepared in advance of halogenation, but some are generated in situ. Reagents specific for electrophilic halogenation include but are not limited to N-chlorosuccinimide (6-12) (NCS), N-chloroammonium salts (13), tert-butylhypochlorite (14), sodium chlorite/(salen)Mn(III) complex (15), chlorine trifluoromethanesulfonate (16), and triethylammonium trichloride (17), for chlorination, N-bromosuccinimide (8-12) and alkylammonium tribromide (18) for bromination, N-iodosuccinimide (19), iodine(l) triflate (20), and dichlorohypoiodite salts (21) for iodination, and various -NF, -XeF, and -OF agents for fluorination (6, 22).
Reagents which are known to deliver electrophilic thiocyanogen include thiocyanogen (23, 24), cyanogen chloride (25-28), and metal thiocyanates mediated by aryliodite (29), NCS (30, 31), and NBS (31, 32).
Electrophilic nitration can be accomplished using a variety of techniques (1). In particular, reagents available include nitronium salts (33-37), methyl nitrate (38), and sodium nitrite mediated by trifluoroacetic acid (39).
Zupan et al. (40) discloses an electrophilic fluorination agent functioning as a mediator in affecting electrophilic reactions. In this reference, mixtures of anisole, Selectfluor.TM. (i.e., 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2. 2]octane-bis(tetrafluoroborate), hereinafter referred to as F-TEDA-BF.sub.4) and I.sub.2, KI, Me.sub.3 Sil, or Mel in solution were shown to produce iodo anisole derivatives regioselectively. This result is not surprising, however, since it has been established that F-TEDA-BF.sub.4 readily and immediately oxidizes iodide to iodine in solution (39).
There is a general need for effective methodologies for introducing various functional groups into aromatic systems. In particular, electrophilic methodologies find widespread applications since these reactions are very well understood and the product distribution is generally predictable. Despite the importance of synthetic methods for introducing electrophiles into aromatic systems, relatively few reagents are available to accomplish such transformations, and moreover, the reagents themselves can be difficult to prepare and use.
Accordingly, it would be desirable to provide an easily employed and generally applicable method for introducing electrophilic groups, E.sup.+, into a variety of aromatic systems.
All references cited herein are incorporated herein by reference in their entireties.